How do I enable prefetching on a cache miss

As mentioned in the Moovweb Developer Docs,

By default, the XDN will only serve prefetch requests from the edge cache. If a request cannot be served from the cache, a 412 status is returned. This protects your origin servers from additional traffic associated with prefetching.

How do I enable serving all prefetch requests regardless of whether or not the request can be served from the edge so that I can improve front end performance and warm my cache?